Conventionally, a RAID (Redundant Arrays of Independent (Inexpensive) Disks) device is widely known as a technology for building a high-speed, high-capacity, highly-reliable disk system by combining a plurality of disks.
In such a RAID device, a plurality of disks, objects to be supported, may differ in actual capacity from one another, and therefore the other disks may not be able to be used as a maintenance part. For example, as illustrated in FIG. 16, a failure occurs in a disk A with an actual capacity of 1010 gigabytes (GB), and a disk B with an actual capacity of 1001 GB is used as a maintenance part of the disk A. In this case, the actual capacity of the disk B is lower than that of the disk A, so the disk B cannot be used as a maintenance part.
To cope with such a situation, a RAID device sets and stores a capacity range of disks to be supported in a FIRM, and supports only a disk meeting the capacity range. For example, as illustrated in FIG. 17, the RAID device stores a “capacity range” indicating a range of actual capacity of a disk and a “defined capacity” indicating a capacity defined for treating disks belonging to the capacity range as a disk with the same capacity in an associated manner.
For example, as illustrated in FIG. 17, when a disk A with an actual capacity of 1010 GB, a disk B with an actual capacity of 1001 GB, and a disk C with an actual capacity of 1100 GB are recognized by the RAID device, the disks A, B, and C belong to a capacity range of “1000 to 1499 GB”. Since a defined capacity corresponding to the capacity range of “1000 to 1499 GB” is “1000 GB”, in the RAID device, the disks A, B, and C are used as a disk with the same capacity of “1000 GB”. Therefore, as illustrated in FIG. 18, when a failure occurs in the disk A with the actual capacity of 1010 GB, even if the disk B with the actual capacity of 1001 GB, which is a slightly different from that of the disk A, is used as a maintenance part of the disk A, the disk B can be used as a maintenance part because they are treated as a disk with the same capacity of 1000 GB.
When a disk vendor releases a disk with a capacity in a new capacity range, and the disk is added to the RAID device, there may be a large difference between an actual capacity and a defined capacity. For example, as illustrated in FIG. 19, the RAID device is programmed to treat a disk with an actual capacity in a capacity range of “1500 GB or higher” as a disk with a defined capacity of “1500 GB”. In such a RAID device, if a disk of which the nominal capacity, which is given as a rough indication of classification of the disk, is 2000 GB and the actual capacity is 2050 GB in a new capacity range is added, the disk with the actual capacity of 2050 GB is recognized as a 1500 GB disk.
Consequently, there is known a technology of revising a device program for adding a new defined capacity when a disk with a capacity in a new capacity range is added. For example, as illustrated in FIG. 20, when a new capacity disk is added, a RAID device revises a device program thereby adding a defined capacity of 2000 GB or higher and a capacity range of 2000 GB or higher. Therefore, when a disk of which the nominal capacity is 2000 GB and the actual capacity is 2050 GB is added, the disk is recognized as a new disk with a defined capacity of 2000 GB.
However, in the above-described technology of revising the device program, it is not known which capacity range of a disk will be added in advance, so it is not possible to determine a capacity range in advance. Therefore, each time a new capacity disk is provided, the device program for adding a defined capacity corresponding to the new capacity disk is revised; thus, there is a problem that it is not possible to easily mount a new capacity disk.
Furthermore, if disks of which the nominal capacities are in the same nominal capacity range although respective actual capacities fall within different capacity ranges are mounted, the RAID device treats the disk in the higher capacity range as a disk with a one level lower capacity; thus, there is a problem that an inappropriate defined capacity is assigned to the disk.
For example, as illustrated in FIG. 21, even though a disk with an actual capacity of 1005 GB and a disk with an actual capacity of 999 GB are the same nominal capacity of 1000 GB, the RAID device recognizes the disks as disks with different defined capacities from each other. Therefore, there is a problem that a capacity that a user can use is reduced, and as a result, an inappropriate defined capacity is assigned to a disk.
Patent Document 1: Japanese Laid-open Patent Publication No. 09-288547
Patent Document 2: Japanese Laid-open Patent Publication No. 08-63298